Actually,
The measurement of black powder is based off a very old blending of weights and measurements systems. The “inaccuracy” stems from the use of a medieval measurement system which couldn't be what we would call very precise (and started out being used for cloth), and is being applied to a dry commodity, black powder.
In the 1200’s, international trade used a system created by the Hanseatic League of merchants, where they used the term “pound” which was divided into 16 ounces, and 7200 “grains””¦, and this was mostly used to weigh wool fabric. So the ounce in this system was 450 grains.
At the same time, weighing of precious metals was done in Britain using the Tower Pound of 5900 grains, divided into 12 units, also labeled ounces. So the “ounce” in this system was 491 grains.
This is assuming, of course, that everybody used a standardized “grain” as the lowest unit”¦, but it wasn’t standardized by our thinking.
THEN in 1303 the avoirdupois weight system appears in a book in England (probably having begun to catch on decades prior), and it shows a pound of 6992 grains, a stone of 14 pounds, a woolsack of 26 stone, an ounce of 1â„16 pound, and finally, the ounce was further broken into 16 parts. So in this case, the pound when divided into 16 ounces gives us an ounce of 437 grains. (sound familiar?)
In 1588 (so almost 300 years later) Queen Elizabeth rounded up the weight of the [avoirdupois] pound to 7000 grains using the troy grain as the standard for the 1â„16th of an ounce, thus adding the “grain” to the avoirdupois weight system, and giving us an ounce = 437.5 grains”¦, which we have today. In the 18th century, then 1â„16th of the new “ounce” was named the "drachm". Which later was *******ized into the “dram”, and if you take the ounce of Queen Elizabeth’s 7000 grain pound, and divide it by 16, you get a dram of 27.34 grains.
Even though Britain and the United States begin to differ over weights and measures by 1824, this old system, designed to weigh dry goods when first implemented centuries before, continued to be used for gunpowder (a 500 year old system, last updated two centuries in the past).
This system continued well into the 20th century. When one looks at a box of shotgun shells from the 1970’s or earlier, you will find “dram equivalent” listed on the box.
So”¦, it’s inaccurate from the beginning since they simply couldn’t be as precise as we are today. I would venture to guess that they didn’t notice the new “ounce” of Queen Elizabeth was .5 grains heavier than the previous ounce. The dram was probably thought to be 27 grains, not 27.34. Luckily, it didn't matter much when shooting.
So for measuring gun powder, now called black powder, the system is lacking precision. It’s quite possible that if we were using English powder of the 18th century, we might find that it is indeed very near to a correct “weight” when using their volume measures. BUT”¦, since refinement of ingredients, and better formula for making powder have been implemented, the 18th century powder appears “weaker”, and our comparisons for volume vs. weight show lots of inaccuracy and inconsistency.
So”¦, IF you use the powder as specified in the text of old manuals for musket cartridges, you get a very “stout” load today. Powder components also differ today than back then, not to mention uniformity of granulation sizes, moisture control, and graphite glazing, so powders made in different parts of the world have different densities and you get different weights when using a volume container to generate an amount. Thus Swiss is hotter than standard Goex, which is hotter than Diamondback, and that’s still “hotter” than the British powder of the AWI if reports are correct.
LD